1. Field of the Invention
The present invention generally relates to dielectric fluids used in capacitors and, in particular, two such fluids which include dioctyl phthalate.
2. Statement of the Prior Art
In the manufacturing of high voltage capacitors, such as those used in appliances like microwave ovens, the selection of the dielectric fluid has a substantial influence on the electrical characteristics of the capacitor. Voltages, in such applications, are commonly within the range of 1000 to 2500 volts. Therefore, it is necessary that the dielectric fluid have a relatively high corona start voltage and a relatively high corona extinguish voltage. The dielectric fluid should further have as high a dielectric constant as practical in order to provide volumetric efficiency to the capacitor. Physically, the fluid must have a relatively low viscosity to enable it to permeate the capacitor winding and fill the voids between the electrodes and the dielectric material. The fluid should also be refinable to achieve low losses in the dielectric during operation. For many years, polychlorinated biphenyls, hereinafter PCBs, have been used as at least part of dielectric fluids because of their ability to satisfy the above requirements. However, PCBs have recently been associated with ecological problems, restrictive use limitations and rising costs. Therefore, suitable substitutes are necessary if these problems are to be avoided. Difficulty is encountered, however, in finding fluids which have comparable performance characteristics to meet the above requirements.
One material which has met with some success in meeting these requirements is a phthalate ester called dioctylphthalate, or more specifically, 2-ethyl-hexyl phthalate (hereinafter DOP). As per the present invention, it has been found that the performance characteristics of capacitors made with DOP as the dielectric fluid can be improved in high voltage applications.